Abstract 383: Paired Immunoglobin-Like Receptor B Regulates Platelet Activation
Introduction: Many of the immunoglobulin (Ig) super family proteins are expressed on platelet surface, and involve in the regulation of platelet activation. Murine paired immunoglobulin-like receptors B (PIRB), as the ortholog of human leukocyte immunoglobulin-like receptors LILRB2 or LILRB3, bearing extracellular Ig-like domains and immunoreceptor tyrosine-based inhibitory motifs, is broadly expressed and plays important roles in immune responses, neuron axonal regeneration and hematopoietic processes. The expressions and functions of PIRB in platelet remain unknown.
Hypothesis: PIRB regulates platelet activation.
Methods: PIRB intracellular domain deletion mice (PIRB-TM) were used to elucidate the functions of PIRB in platelet activation.
Results: We found that LILRB2 and LILRB3 (or PIRB) expressed in human (or mouse) platelets. The Increasing megakaryocytes ratio in bone marrow and mild thrombocythemia were observed in PIRB-TM mice. Deficiency of PIRB facilitated agonists-induced platelet aggregation and spreading on immobilized fibrinogen (Fg). The rate of clot retraction in platelet-rich plasma containing PIRB-TM platelets was also enhanced. Further signaling analysis revealed that PIRB bound to SHP1 and SHP2. And collagen related peptide (CRP)-induced tyrosine phosphorylation of LAT, SLP76 and PLCγ2 increased in PIRB-TM platelet. The phosphorylation of FAK Y397 and integrin β3 Y785, but not integrin β3 Y773, was also enhanced in PIRB-TM platelet spread on immobilized Fg. We also found that one of the PIRB ligands angiopoietin like protein 2 (Angptl2) was highly expressed and stored in platelet α-granule, and was able to be released and attached to platelet surface upon platelet activation. Purified Angptl2 inhibited agonists-induced human platelet aggregation and spreading on immobilized Fg. Angptl2 inhibited CRP-induced phosphorylation of LAT, SLP76 and PLCγ2, and spreading-driven phosphorylation of FAK Y397 and integrin β3 Y785 in platelet.
Conclusions: These results revealed that PIRB and its ligand Angptl2 attenuated platelet activation by suppression of GPVI-mediated and integrin αIIbβ3 mediated outside-in signaling. Therefore, LILRB2 and LILRB3 may prove to be the new promising antithrombotic targets.
Author Disclosures: X. Fan: None. P. Shi: None. J. Dai: None. Y. Lu: None. K. Wang: None. J. Zhang: None. J. Zheng: None. J. Liu: None.
- © 2014 by American Heart Association, Inc.